1. Field of the Invention
The present invention relates to a method for controlling operation of a cylinder apparatus. In particular, the present invention relates to a method for controlling operation of a cylinder apparatus, which makes it possible to displace a piston of the cylinder apparatus under the action of a pressure fluid and a driving section.
2. Description of the Related Art
A cylinder apparatus has been hitherto used, for example, such that a workpiece is attached to an end of a piston rod arranged for a cylinder, and pressure fluid is supplied to a cylinder chamber of the cylinder to displace the piston rod under the pressing action of the pressure fluid. Accordingly, the workpiece is transported and positioned at a target position.
When the workpiece is displaced by such a cylinder apparatus, the workpiece having a large load can be displaced, because output is large owing to the pressure fluid. However, it has been difficult to highly accurately position a workpiece, because pressure fluid is compressive fluid.
On the other hand, the following method is known. That is, a workpiece is attached to a ball screw provided for a cylinder apparatus, and the ball screw is rotated by a rotary driving source (for example, a motor) to displace the workpiece thereby. The operation is electrically controlled, and thus the workpiece is positioned highly accurately with respect to a target position.
A cylinder apparatus has been suggested, which is provided with both of the driving force brought about when the workpiece is displaced by the pressure fluid as described above and the positioning accuracy for the workpiece brought about under the driving action of the rotary driving source (see, for example, Japanese Laid-Open Patent Publication No. 9-210014).
In the case of the conventional technique disclosed in Japanese Laid-Open Patent Publication No. 9-210014, for example, load, which is exerted on the cylinder apparatus, is sometimes fluctuated, for example, due to the fluctuation of weight of a workpiece, when the cylinder apparatus is driven and/or when the cylinder apparatus is stopped. In such a situation, the amount of the pressure fluid supplied to the cylinder apparatus is increased/decreased in response to the fluctuation of the load of the workpiece, and driving force of the piston is changed to correspond to the load. However, it is difficult to instantaneously increase/decrease the amount of the pressure fluid supplied in response to the fluctuation of the load.
On the other hand, the driving force, which corresponds to the fluctuation of the load, can be obtained by instantaneously increasing/decreasing the driving torque of the rotary driving source by electric control. However, in this case, it is necessary that the rotary driving source having a large driving torque is previously provided in order to respond to fluctuation of the load brought about in the cylinder apparatus. Therefore, the rotary driving source is consequently large-sized, and the production cost of the cylinder apparatus is increased.
Further, large-sized rotary driving source is not required during ordinary operation in which the fluctuation of the load is not caused in the cylinder apparatus. Therefore, when a large-sized rotary driving source is always driven, unnecessary electricity is excessively consumed.
In recent years, it has been demanded to realize a smaller size of the cylinder apparatus, for example, to be installed in a small space in the cylinder apparatus.